Sinks in the photographic darkroom should be sized adequately and constructed properly. Most sinks in Navy labs are factory-made and meet all the requirements for photographic work Sinks should be big enough and built so they drain thoroughly. The sink should have duckbords to keep trays and tanks off the bottom and to permit water to circulate under and around the solution tanks to maintain correct and constant temperatures. Sinks, also, should have a mixing valve to control the temperature of the water in the sink and a

Figure 10-1. Photographic processing sink

standpipe to hold water in the sink at the correct depth, yet still allow water to flow out (fig. 10-1).

SAFELIGHTS

The function of a safelight is to transmit the maximum amount of light that can be used safely without damaging the sensitized materials being processed. The color sensitivity of different sensitized materials varies. Therefore, the color and intensity of transmitted light must be varied accordingly. A darkroom safelight is the combination of a rated light source and a filter designated to protect a specific sensitized material.

The word safe. of course, is a relative term since no sensitized photographic materials are ever completely safe from the effects of safelight illumination. However, a filtered light is accepted as safe when the sensitized materials can be handled under the illumination with no evidence of fogging for at least twice as long as the normal processing time. No procedures must be followed precisely when safelights are used:

Use only the size of incandescent bulb specified; for example, 7 1/2 watt, 15 watt, or 25 watt.

Handle sensitized material at the distance recommended by the manufacturer. This is usually between 3 and 6 feet.

To determine whether a safelight is safe, you should follow these procedures:

1. In the dark, place a sheet of unexposed film, emulsion-side up, on the working area where the film is to be processed.

2. Place several coins on the emulsion and turn on the safelight. Leave the safelight on for twice the length of time the film will normally be processed.

3. Process the film normally and check to see whether there is less density in the areas covered by the coins. When there is less density, it indicates the film was fogged by the safelight and the safelight is not safe. A safelight that causes fogging may be corrected by replacing the filter, by installing a lower rated bulb, or

Figure 10-2. Safelights.

by increasing the distance between the safelight and the material. Safelight filters are covered in chapter 3.

A safelight is most efficient when its output of illumination is indirect or reflected. When the safelight is not constructed on the indirect principle, it should never be pointed directly at the sensitized material; it should be placed so the light beam is away from or at an angle to the sensitized material. Figure 10-2 shows safelights used in photographic darkrooms.